Activity and abundance of ammonia oxidizing bacteria and archaea in Bolivian soils

Introduction
Understanding the relationship between soil biodiversity, microbial abundance and ecosystem function remains a challenging issue. Ammonia oxidation, the first, rate-limiting step of nitrification, is performed by bacteria (AOB) and archaea (AOA), but their relative contribution to ammonia oxidation is not yet understood. Here we investigate nitrification and abundance of AOA and AOB in soils under potato cultivation, eucalyptus and fallow land uses in Bolivia.
Objectives
• Assess differences in activity and abundance of AOB and AOA in potato, fallow fields, and eucalyptus plantations (Cochabamba, Bolivia).
• Evaluate the relationships between activity and abundance of AOB and AOA
Methods
One composite soil sample was taken in each of 8 replicate 0.5 - 1 ha potato, fallow and eucalyptus plots (Chullchunqani Community, Pocona, Cochabamba-Bolivia). Net nitrogen mineralization and net nitrification were measured with an aerobic laboratory incubation essay. Potential nitrification was determined by the shaken soil slurry method, with and without 100 M allylthiourea (ATU), a bacterial and eukaryotic protein synthesis inhibitor. AOA or AOB amoA gene copy abundance were assessed through real-time PCR.
Results
Potential nitrification of AOB and AOA, net N mineralization and nitrification were significantly lower under eucalyptus compared to potato soils. AOA abundance was lower under eucalyptus and fallow compared to potato, but there were no significant differences for AOB. AOA accounted for 93 to 98% of total amoA gene copy numbers. AOB and AOA abundances were positively correlated both with total and their respective potential nitrification rates.
Conclusions
This study demonstrated dominance of AOA amoA gene copies in Bolivian soils under 3 land uses. Potential nitrification was significantly correlated with the abundance of AOB and AOA. Eucalyptus plantations led to lower process rates and abundance.